Method and Apparatus for reporting buffer status report by RRC_INACTIVE state UE in mobile wireless communication system

ABSTRACT

A method and apparatus for data transfer in RRC_INACTIVE state is provided. Method for data transfer in RRC_INACTIVE state includes receiving configuration information for second resume procedure, initiating second resume procedure and transmitting an uplink RRC message together with data in a MAC PDU. During the procedure, specific radio bearers are resumed and MAC CE are transmitted for data transmission.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2021-0109006, filed on Aug. 18, 2021, the disclosureof which is incorporated herein by reference in its entirety.

BACKGROUND

The present disclosure relates to a mobile communication system withdata transfer in RRC_INACTIVE state. More specifically, the presentdisclosure relates to resume procedure initiation for data transferduring RRC_INACTIVE and determination on radio bearers for data transferduring RRC_INACTIVE.

To meet the increasing demand for wireless data traffic since thecommercialization of 4th generation (4G) communication systems, the 5thgeneration (5G) system is being developed. For the sake of high, 5Gsystem introduced millimeter wave (mmW) frequency bands (e.g. 60 GHzbands). In order to increase the propagation distance by mitigatingpropagation loss in the 5G communication system, various techniques areintroduced such as beamforming, massive multiple-input multiple output(MIMO), full dimensional MIMO (FD-MIMO), array antenna, analogbeamforming, and large-scale antenna. In addition, base station isdivided into a central unit and plurality of distribute units for betterscalability. To facilitate introduction of various services, 5Gcommunication system targets supporting higher data rate and smallerlatency.

SUMMARY

Aspects of the present disclosure are to address the problems of statetransition from RRC_INACTIVE to RRC_CONNECTED for data transfer.Accordingly, an aspect of the present disclosure is to provide a methodand an apparatus for data transfer in RRC_INACTIVE state. In accordancewith an aspect of the present disclosure, a method of a terminal inmobile communication system is provided. In the method, UE receives froma first base station a RRCRelease message including a first informationfor a second resume procedure, determines a first radio bearer groupbased on the first information for a second procedure, receives from asecond base station a system information including a second informationfor a second resume procedure, initiate the second resume procedure,re-establishes PDCP entities of radio bearers of a second radio bearergroup, resume radio bearers of the second radio bearer group, transmitsto the second base station a RRCResumeRequest message and receives fromthe second base station a RRCResume message.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram illustrating the architecture of an 5G system and aNG-RAN to which the disclosure may be applied;

FIG. 1B is a diagram illustrating a wireless protocol architecture in an5G system to which the disclosure may be applied;

FIG. 1C is a diagram illustrating an RRC state transition.

FIG. 2A is a diagram illustrating operations of a terminal and a basestation according to an embodiment of the present invention.

FIG. 2B is a diagram illustrating a first resume procedure and a secondresume procedure according to an embodiment of the present invention.

FIG. 2C is a diagram illustrating a structure of an uplink MAC PDU usedin a second resume procedure.

FIG. 2D is a diagram illustrating a structure of a general uplink MACPDU.

FIG. 2E is a diagram illustrating a hierarchical structure of securitykeys.

FIG. 2F is a diagram illustrating structures of a first BSR MAC CE and asecond BSR MAC CE.

FIG. 2G is a diagram illustrating structures of a third BSR MAC CE and afourth BSR MAC CE.

FIG. 2H is a diagram illustrating a MAC-I calculation process andciphering process.

FIG. 3A is a flow diagram illustrating an operation of a terminal.

FIG. 4A is a block diagram illustrating the internal structure of a UEto which the disclosure is applied.

FIG. 4B is a block diagram illustrating the configuration of a basestation according to the disclosure.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the present disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thepresent disclosure. In addition, descriptions of well-known functionsand constructions may be omitted for clarity and conciseness.

The terms used, in the following description, for indicating accessnodes, network entities, messages, interfaces between network entities,and diverse identity information is provided for convenience ofexplanation. Accordingly, the terms used in the following descriptionare not limited to specific meanings but may be replaced by other termsequivalent in technical meanings.

In the following descriptions, the terms and definitions given in the3GPP standards are used for convenience of explanation. However, thepresent disclosure is not limited by use of these terms and definitionsand other arbitrary terms and definitions may be employed instead.

Table 1 lists the acronyms used throughout the present disclosure.

TABLE 1 Acronym Full name 5GC 5G Core Network ACK Acknowledgement AMAcknowledged Mode AMF Access and Mobility Management Function ARQAutomatic Repeat Request AS Access Stratum ASN.1 Abstract SyntaxNotation One BSR Buffer Status Report BWP Bandwidth Part CA CarrierAggregation CAG Closed Access Group CG Cell Group C-RNTI Cell RNTI CSIChannel State Information DCI Downlink Control Information DRB (user)Data Radio Bearer DRX Discontinuous Reception HARQ Hybrid AutomaticRepeat Request IE Information element LCG Logical Channel Group MACMedium Access Control MIB Master Information Block NAS Non-AccessStratum NG-RAN NG Radio Access Network NR NR Radio Access PBRPrioritised Bit Rate PCell Primary Cell PCI Physical Cell IdentifierPDCCH Physical Downlink Control Channel PDCP Packet Data ConvergenceProtocol PDSCH Physical Downlink Shared Channel PDU Protocol Data UnitPHR Power Headroom Report PLMN Public Land Mobile Network PRACH PhysicalRandom Access Channel PRB Physical Resource Block PSS PrimarySynchronisation Signal PUCCH Physical Uplink Control Channel PUSCHPhysical Uplink Shared Channel RACH Random Access Channel RAN RadioAccess Network RA-RNTI Random Access RNTI RAT Radio Access Technology RBRadio Bearer RLC Radio Link Control RNA RAN-based Notification Area RNAURAN-based Notification Area Update RNTI Radio Network TemporaryIdentifier RRC Radio Resource Control RRM Radio Resource Management RSRPReference Signal Received Power RSRQ Reference Signal Received QualityRSSI Received Signal Strength Indicator SCell Secondary Cell SCSSubcarrier Spacing SDAP Service Data Adaptation Protocol SDU ServiceData Unit SFN System Frame Number S-GW Serving Gateway SI SystemInformation SIB System Information Block SpCell Special Cell SRBSignalling Radio Bearer SRS Sounding Reference Signal SSB SS/PBCH blockSSS Secondary Synchronisation Signal SUL Supplementary Uplink TMTransparent Mode UCI Uplink Control Information UE User Equipment UMUnacknowledged Mode

Table 2 lists the terminologies and their definition used throughout thepresent disclosure.

TABLE 2 Terminology Definition allowedCG-List List of configured grantsfor the corresponding logical channel. This restriction applies onlywhen the UL grant is a configured grant. If present, UL MAC SDUs fromthis logical channel can only be mapped to the indicated configuredgrant configuration. If the size of the sequence is zero, then UL MACSDUs from this logical channel cannot be mapped to any configured grantconfigurations. If the field is not present, UL MAC SDUs from thislogical channel can be mapped to any configured grant configurations.allowedSCS-List List of allowed sub-carrier spacings for thecorresponding logical channel. If present, UL MAC SDUs from this logicalchannel can only be mapped to the indicated numerology. Otherwise, ULMAC SDUs from this logical channel can be mapped to any configurednumerology. allowedServingCells List of allowed serving cells for thecorresponding logical channel. If present, UL MAC SDUs from this logicalchannel can only be mapped to the serving cells indicated in this list.Otherwise, UL MAC SDUs from this logical channel can be mapped to anyconfigured serving cell of this cell group. Carrier frequency centerfrequency of the cell. Cell combination of downlink and optionallyuplink resources. The linking between the carrier frequency of thedownlink resources and the carrier frequency of the uplink resources isindicated in the system information transmitted on the downlinkresources. Cell Group in dual connectivity, a group of serving cellsassociated with either the MeNB or the SeNB. Cell reselection A processto find a better suitable cell than the current serving cell based onthe system information received in the current serving cell Cellselection A process to find a suitable cell either blindly or based onthe stored information Dedicated signalling Signalling sent on DCCHlogical channel between the network and a single UE. discardTimer Timerto control the discard of a PDCP SDU. Starting when the SDU arrives.Upon expiry, the SDU is discarded. F The Format field in MAC subheaderindicates the size of the Length field. Field The individual contents ofan information element are referred to as fields. Frequency layer set ofcells with the same carrier frequency. Global cell identity An identityto uniquely identifying an NR cell. It is consisted of cellIdentity andplmn-Identity of the first PLMN-Identity in plmn-IdentityList in SIB1.gNB node providing NR user plane and control plane protocol terminationstowards the UE, and connected via the NG interface to the 5GC. Handoverprocedure that changes the serving cell of a UE in RRC_CONNECTED.Information element A structural element containing single or multiplefields is referred as information element. L The Length field in MACsubheader indicates the length of the corresponding MAC SDU or of thecorresponding MAC CE LCID 6 bit logical channel identity in MACsubheader to denote which logical channel traffic or which MAC CE isincluded in the MAC subPDU MAC-I Message Authentication Code -Integrity. 16 bit or 32 bit bit string calculated by NR IntegrityAlgorithm based on the security key and various fresh inputs Logicalchannel a logical path between a RLC entity and a MAC entity. There aremultiple logical channel types depending on what type of information istransferred e.g. CCCH (Common Control Channel), DCCH (Dedicate ControlChannel), DTCH (Dedicate Traffic Channel), PCCH (Paging Control Channel)LogicalChannelConfig The IE LogicalChannelConfig is used to configurethe logical channel parameters. It includes priority,prioritisedBitRate, allowedServingCells, allowedSCS-List,maxPUSCH-Duration, logicalChannelGroup, allowedCG-List etclogicalChannelGroup ID of the logical channel group, as specified in TS38.321, which the logical channel belongs to MAC CE Control Elementgenerated by a MAC entity. Multiple types of MAC CEs are defined, eachof which is indicated by corresponding LCID. A MAC CE and acorresponding MAC sub-header comprises MAC subPDU Master Cell Group inMR-DC, a group of serving cells associated with the Master Node,comprising of the SpCell (PCell) and optionally one or more SCells.maxPUSCH-Duration Restriction on PUSCH-duration for the correspondinglogical channel. If present, UL MAC SDUs from this logical channel canonly be transmitted using uplink grants that result in a PUSCH durationshorter than or equal to the duration indicated by this field.Otherwise, UL MAC SDUs from this logical channel can be transmittedusing an uplink grant resulting in any PUSCH duration. NR NR radioaccess PCell SpCell of a master cell group. PDCP entity The processtriggered upon upper layer request. It includes the reestablishmentinitialization of state variables, reset of header compression andmanipulating of stored PDCP SDUs and PDCP PDUs. The details can be foundin 5.1.2 of 38.323 PDCP suspend The process triggered upon upper layerrequest. When triggered, transmitting PDCP entity set TX_NEXT to theinitial value and discard all stored PDCP PDUs. The receiving entitystop and reset t-Reordering, deliver all stored PDCP SDUs to the upperlayer and set RX_NEXT and RX_DELIV to the initial value PDCP-config TheIE PDCP-Config is used to set the configurable PDCP parameters forsignalling and data radio bearers. For a data radio bearer,discardTimer, pdcp-SN-Size, header compression parameters, t-Reorderingand whether integrity protection is enabled are configured. For asignaling radio bearer, t- Reordering can be configured PLMN ID Checkthe process that checks whether a PLMN ID is the RPLMN identity or anEPLMN identity of the UE. Primary Cell The MCG cell, operating on theprimary frequency, in which the UE either performs the initialconnection establishment procedure or initiates the connectionre-establishment procedure. Primary SCG Cell For dual connectivityoperation, the SCG cell in which the UE performs random access whenperforming the Reconfiguration with Sync procedure. priority Logicalchannel priority, as specified in TS 38.321. an integer between 0 and 7.0 means the highest priority and 7 means the lowest priority PUCCH SCella Secondary Cell configured with PUCCH. Radio Bearer Logical pathbetween a PDCP entity and upper layer (i.e. SDAP entity or RRC) RLCbearer RLC and MAC logical channel configuration of a radio bearer inone cell group. RLC bearer The lower layer part of the radio bearerconfiguration configuration comprising the RLC and logical channelconfigurations. RX_DELIV This state variable indicates the COUNT valueof the first PDCP SDU not delivered to the upper layers, but stillwaited for. RX_NEXT This state variable indicates the COUNT value of thenext PDCP SDU expected to be received. RX_REORD This state variableindicates the COUNT value following the COUNT value associated with thePDCP Data PDU which triggered t-Reordering. Serving Cell For a UE inRRC_CONNECTED not configured with CA/DC there is only one serving cellcomprising of the primary cell. For a UE in RRC_CONNECTED configuredwith CA/DC the term ‘serving cells’ is used to denote the set of cellscomprising of the Special Cell(s) and all secondary cells. SpCellprimary cell of a master or secondary cell group. Special Cell For DualConnectivity operation the term Special Cell refers to the PCell of theMCG or the PSCell of the SCG, otherwise the term Special Cell refers tothe PCell. SRB Signalling Radio Bearers″ (SRBs) are defined as RadioBearers (RBs) that are used only for the transmission of RRC and NASmessages. SRB0 SRB0 is for RRC messages using the CCCH logical channelSRB1 SRB1 is for RRC messages (which may include a piggybacked NASmessage) as well as for NAS messages prior to the establishment of SRB2,all using DCCH logical channel; SRB2 SRB2 is for NAS messages and forRRC messages which include logged measurement information, all usingDCCH logical channel. SRB2 has a lower priority than SRB1 and may beconfigured by the network after AS security activation; SRB3 SRB3 is forspecific RRC messages when UE is in (NG)EN- DC or NR-DC, all using DCCHlogical channel SRB4 SRB4 is for RRC messages which include applicationlayer measurement reporting information, all using DCCH logical channel.Suitable cell A cell on which a UE may camp. Following criteria applyThe cell is part of either the selected PLMN or the registered PLMN orPLMN of the Equivalent PLMN list The cell is not barred The cell is partof at least one TA that is not part of the list of “Forbidden TrackingAreas for Roaming” (TS 22.011 [18]), which belongs to a PLMN thatfulfils the first bullet above. The cell selection criterion S isfulfilled (i.e. RSRP and RSRQ are better than specific valuest-Reordering Timer to control the reordering operation of received PDCPpackets. Upon expiry, PDCP packets are processed and delivered to theupper layers. TX_NEXT This state variable indicates the COUNT value ofthe next PDCP SDU to be transmitted. UE Inactive AS UE Inactive ASContext is stored when the connection is Context suspended and restoredwhen the connection is resumed. It includes information below. thecurrent KgNB and KRRCint keys, the ROHC state, the stored QoS flow toDRB mapping rules, the C-RNTI used in the source PCell, the cellIdentityand the physical cell identity of the source PCell, thespCellConfigCommon within ReconfigurationWithSync of the NR PSCell (ifconfigured) and all other parameters configured except for: parameterswithin ReconfigurationWithSync of the PCell; parameters withinReconfigurationWithSync of the NR PSCell, if configured; parameterswithin MobilityControlInfoSCG of the E-UTRA PSCell, if configured;servingCellConfigCommonSIB;

In the present invention, “trigger” or “triggered” and “initiate” or“initiated” may be used in the same meaning.

In the present invention, “radio bearers allowed for the second resumeprocedure”, “radio bearers for which the second resume procedure isset”, and “radio bearers for which the second resume procedure isenabled” may all have the same meaning.

FIG. 1A is a diagram illustrating the architecture of an 5G system and aNG-RAN to which the disclosure may be applied. 5G system consists ofNG-RAN (1 a-01) and 5GC (1 a-02). An NG-RAN node is either:

-   -   a gNB, providing NR user plane and control plane protocol        terminations towards the UE; or    -   an ng-eNB, providing E-UTRA user plane and control plane        protocol terminations towards the UE.

The gNBs (1 a-05 or 1 a-06) and ng-eNBs (1 a-03 or 1 a-04) areinterconnected with each other by means of the Xn interface. The gNBsand ng-eNBs are also connected by means of the NG interfaces to the 5GC,more specifically to the AMF (Access and Mobility Management Function)and to the UPF (User Plane Function). AMF (1 a-07) and UPF (1 a-08) maybe realized as a physical node or as separate physical nodes.

A gNB (1 a-05 or 1 a-06) or an ng-eNBs (1 a-03 or 1 a-04) hosts thefunctions listed below.

Functions for Radio Resource Management such as Radio Bearer Control,Radio Admission Control, Connection Mobility Control, Dynamic allocationof resources to UEs in uplink, downlink and sidelink (scheduling); and

IP and Ethernet header compression, uplink data decompression andencryption of user data stream; and

Selection of an AMF at UE attachment when no routing to an MME can bedetermined from the information provided by the UE; and

Routing of User Plane data towards UPF; and

Scheduling and transmission of paging messages; and Scheduling andtransmission of broadcast information (originated from the AMF or O&M);and

Measurement and measurement reporting configuration for mobility andscheduling; and

Session Management; and

QoS Flow management and mapping to data radio bearers; and

Support of UEs in RRC_INACTIVE state; and

Radio access network sharing; and

Tight interworking between NR and E-UTRA; and

Support of Network Slicing.

The AMF (1 a-07) hosts the functions such as NAS signaling, NASsignaling security, AS security control, SMF selection, Authentication,Mobility management and positioning management.

The UPF (1 a-08) hosts the functions such as packet routing andforwarding, transport level packet marking in the uplink, QoS handlingand the downlink, mobility anchoring for mobility etc.

FIG. 1B is a diagram illustrating a wireless protocol architecture in an5G system to which the disclosure may be applied.

User plane protocol stack consists of SDAP (1 b-01 or 1 b-02), PDCP (1b-03 or 1 b-04), RLC (1 b-05 or 1 b-06), MAC (1 b-07 or 1 b-08) and PHY(1 b-09 or 1 b-10). Control plane protocol stack consists of NAS (1 b-11or 1 b-11 b-), RRC (1 b-13 or 1 b-14), PDCP, RLC, MAC and PHY.

Each protocol sublayer performs functions related to the operationslisted in the table 3.

TABLE 3 Sub- layer Functions NAS authentication, mobility management,security control etc RRC System Information, Paging, Establishment,maintenance and release of an RRC connection, Security functions,Establishment, configuration, maintenance and release of SignallingRadio Bearers (SRBs) and Data Radio Bearers (DRBs), Mobility, QoSmanagement, Detection of and recovery from radio link failure, NASmessage transfer etc. SDAP Mapping between a QoS flow and a data radiobearer, Marking QoS flow ID (QFI) in both DL and UL packets. PDCPTransfer of data, Header compression and decompression, Ciphering anddeciphering, Integrity protection and integrity verification,Duplication, Reordering and in-order delivery, Out-of-order deliveryetc. RLC Transfer of upper layer PDUs, Error Correction through ARQ,Segmentation and re-segmentation of RLC SDUs, Reassembly of SDU, RLCre-establishment etc. MAC Mapping between logical channels and transportchannels, Multiplexing/demultiplexing of MAC SDUs belonging to one ordifferent logical channels into/from transport blocks (TB) deliveredto/from the physical layer on transport channels, Scheduling informationreporting, Priority handling between UEs, Priority handling betweenlogical channels of one UE etc. PHY Channel coding, Physical-layerhybrid-ARQ processing, Rate matching, Scrambling, Modulation, Layermapping, Downlink Control Information, Uplink Control Information etc.

The terminal supports three RRC states. Table 4 lists thecharacteristics of each state.

TABLE 4 RRC state Characteristic RRC_IDLE PLMN selection; Broadcast ofsystem information; Cell re-selection mobility; Paging for mobileterminated data is initiated by 5GC; DRX for CN paging configured byNAS. RRC_INACTIVE PLMN selection; Broadcast of system information; Cellre-selection mobility; Paging is initiated by NG-RAN (RAN paging);RAN-based notification area (RNA) is managed by NG- RAN; DRX for RANpaging configured by NG-RAN; 5GC - NG-RAN connection (both C/U-planes)is established for UE; The UE AS context is stored in NG-RAN and the UE;NG-RAN knows the RNA which the UE belongs to. RRC_CONNECTED 5GC - NG-RANconnection (both C/U-planes) is established for UE; The UE AS context isstored in NG-RAN and the UE; NG-RAN knows the cell which the UE belongsto; Transfer of unicast data to/from the UE; Network controlled mobilityincluding measurements.

FIG. 1C is a diagram illustrating an RRC state transition.

Between RRC_CONNECTED 1 c-11 and RRC_INACTIVE 1 c-13, a state transitionoccurs due to the exchange of the Resume message and the Release messagecontaining the Suspend IE.

A state transition occurs between RRC_CONNECTED 1 c-11 and RRC_IDLE 1c-15 through RRC connection establishment and RRC connection release.

The state transition from RRC_INACTIVE to RRC_CONNECTED involves notonly signal exchange between the terminal and the base station, but alsocontext transfer and data path change between the base stations. If theterminal has enough data to transmit, these additional procedures can besufficiently justified, but if not, excessive overhead can reduce theefficiency of the network.

The present invention introduces a new resumption procedure capable oftransmitting and receiving data without transition to RRC_CONNECTED.Hereinafter, a resume procedure for the purpose of transitioning theterminal to the RRC_CONNECTED state from the RRC_INACTIVE state isreferred to as a first resume procedure, and a procedure fortransmitting and receiving data while the terminal is in theRRC_INACTIVE state is referred to as a second resume procedure. Throughthe first resume procedure, the terminal may resume the suspended RRCconnection, and through the second resumption procedure, the terminalmay resume data transmission and reception. The terminal may switch tothe first resume procedure while performing the second resume procedure.

FIG. 2A is a diagram illustrating operations of a terminal and a basestation according to an embodiment of the present invention.

In a wireless communication system including a terminal 2 a-01, a firstbase station 2 a-03, and a second base station 2 a-05, the terminal andthe base station operate as follows.

In steps 2 a-11, the terminal reports capability to the first basestation or another base station. The UE capability information transferprocedure consists of transmitting an RRC control message calledUECapabilityInformation containing UE capability information to theserving base station if the serving base station transmits an RRCmessage requesting UE capability information. UECapabilityInformationincludes the following information.

<UECapabilityInformation>

1. First information related to RRC_INACTIVE: 1-bit informationindicating whether the terminal supports RRC_INACTIVE. Only one 1-bit isreported regardless of the number of bands supported by the terminal.

2. Second information related to RRC_INACTIVE: information indicatingwhether the second resume procedure is supported or not. It may indicatewhether the second resume procedure is supported for each band supportedby the terminal. When the terminal supports n bands, n 1-bit informationis reported.

3. Various pieces of capability information related to datatransmission/reception between the terminal and the base station (forexample, whether specific decoding is supported, etc.).

The terminal supporting RRC_INACTIVE supports the first resumptionprocedure in all frequency bands supported by the terminal. That is, thefirst information related to RRC_INACTIVE support is information appliedto a plurality of bands, and the second information related toRRC_INACTIVE is information applied to one band. A terminal that doesnot support RRC_INACTIVE does not support the second resumptionprocedure in any frequency band that it supports. The serving basestation provides appropriate NR configuration information to the UE byreferring to the capability of the UE. The UE and the serving basestation transmit and receive data in the RRC_CONNECTED state, and whenthe data transmission and reception are completed, the serving basestation determines to transition the terminal state to the RRC_INACTIVEstate.

In step 2 a-13, the first base station transmits an RRCRelease messageto the terminal. The RRCRelease message includes SuspendConfig IE, andSuspendConfig includes the following information.

<SuspendConfig>

1. The first terminal identifier: an identifier of a terminal that maybe included in the Resume Request when a state transition toRRC_CONNECTED is made. It has a 40-bit length.

2. The second terminal identifier: an identifier of a terminal that maybe included in the Resume Request when a state transition toRRC_CONNECTED is made. It has a 24-bit length.

3. ran-Paging Cycle: Paging cycle to be applied in RRC_INACTIVE state.

4. ran-Notification AreaInfo: Configuration information of aran-Notification Area consisting of a list of cells and the like. Theterminal initiates a resume procedure when the ran_Notification Area ischanged.

5. t380: Timer related to the periodic resumption procedure.

6. NextHopChangingCount (NCC): Counter used to derive new security keysafter performing the resume procedure.

7. Second resume procedure related information: List of DRB s configuredwith second resume procedures, 1-bit information indicating whether thesecond resume procedure is configured for SRB2, 1-bit informationindicating whether the second resume procedure is configured for SRB4,Data size threshold of the second resume procedure (hereinafter referredto as dedicated data threshold), reference signal received powerthreshold of the second resume procedure (hereinafter referred to asdedicated reference signal received power threshold)

Since SRB1 among SRB1, SRB2, SRB3, and SRB4 transmits and receives themost important RRC control message, it is important to quickly transmitthe RRC control message as the second resumption procedure, and thesecond resumption procedure is highly effective for SRB1. SRB2 and SRB4are less important than SRB1 because relatively large messages canoccur, but they still transmit important control messages, so the secondresumption procedure is effective for SRB2 and SRB4. SRB3 is not usedwhen multiple connections are not established. Accordingly, in thepresent invention, a second resumption procedure can be explicitlyconfigured for SRB2 and SRB4. A second resumption procedure is notexplicitly configured for SRB1 and SRB3. If a second resumptionprocedure is configured for at least one radio bearer, a secondresumption procedure is implicitly configured for SRB1. A secondresumption procedure is not configured for SRB3 under any conditions.

In step 2 a-14, the terminal performs the SuspendConfig operation set.The SuspendConfig operation set is applied at a predetermined first orsecond time point. For the SuspendConfig operation set is performed, thefollowing operations are sequentially performed.

<SuspendConfig Operation Set>

1. Apply suspendConfig.

2. Reset MAC.

3. Reset SRB1's RLC entity.

4. All SRBs and DRBs are suspended.

5. Start T380 set to t380.

6. Enter RRC_INACTIVE state.

The terminal applies the first time point for SuspendConfig operationset when the second resume related information is included, and thesecond time point if not included.

The first time point is as follows.

Earlier time point between a time point at which 100 ms has elapsedsince receiving the RRCRelease message and a time point at which thelower layer successfully acknowledged the reception of the RRCReleasemessage.

The second time point is as follows.

Earlier time point between a time point at which 60 ms has elapsed sincereceiving the RRCRelease message and a time point at which the lowerlayer successfully acknowledged the reception of the RRCRelease message.

Different time points are used because the reliability of the RRCRelease message including the second resume-related information shouldbe higher than that of the RRC Release message not including the secondresume information.

In step 2 a-15, the terminal moves to a new cell. The terminal maycompare the radio signal quality of the serving cell and the neighboringcell to reselect the neighboring cell having a better radio signalquality. Alternatively, a cell in which the radio signal quality isgreater than or equal to a certain threshold may be selected.

In steps 2 a-17, the terminal receives system information including SIB1in a new cell. The SIB1 may include at least two types of informationbelow.

<SIB1>

1. The value of t319

2. 1-bit information indicating whether the second resume procedure isallowed (or whether the second resume procedure is configured orpossible).

If the second resume procedure is allowed, the following information isincluded and broadcast in system information (hereinafter, SIBX) otherthan SIB1.

<SIBX>

1. Data size threshold of the second resume procedure (hereinafter,referred to as public data threshold)

2. Reference signal received power threshold of the second resumeprocedure (hereinafter, referred to as a common reference signalreceived power threshold)

3. Random access transmission resource information for the second resumeprocedure.

4. t319ext

The terminal receives the SIBX if there is at least one radio bearerconfigured with a second resume procedure, i.e., if the second resumeprocedure is configured for at least one DRB or if the second resumeprocedure is configured for SRB2 or SRB4.

The terminal receiving the necessary system information including SIB1performs the RRC_INACTIVE operation shown in Table 4 in the cell.

In step 2 a-19, an event that triggers the resume procedure occurs. Whenthe upper layer or AS requests the resumption of the suspended RRCconnection or when new data occurs, the resume procedure may betriggered.

In step 2 a-21, the terminal triggers one of the first resume procedureand the second resume procedure. If any one of the first resumptioncondition sets is satisfied, the first resume procedure is triggered.

<First Resume Condition Set>

1. The upper layer requests the resumption of the suspended RRCconnection.

2. RAN paging including the first identifier is received.

3. RNA update occurs.

4. Data has been generated in the radio bearer that is allowed totrigger the second resumption procedure, but at least one of the secondresume condition set is not satisfied.

If all of the second resume condition sets are satisfied, the secondresume procedure is triggered.

<Second Resume Condition Set>

1. Data available for transmission is generated in a bearer belonging tothe first bearer set.

2. The amount of data available for transmission from the bearerbelonging to the first bearer set is less than the final data threshold.

3. The reference signal received power of the current serving cell ishigher than the final reference signal received power threshold.

4. The current serving cell provides transmission resource for thesecond resume procedure.

A radio bearer triggering second resume procedure is allowed (or asecond resume procedure is allowed) means DRB a second resume procedureis allowed and SRB a second resumption procedure is allowed. SRB3 doesnot allow the second resume procedure, and SRB2 and SRB4 are indicatedby explicit information whether the second resume procedure is allowed.When the second resume procedure is allowed in at least one radiobearer, the second resume procedure is automatically allowed in theSRB1.

The final data threshold is the lower of the dedicated data thresholdand the common data threshold or alternatively the dedicated datathreshold, if there are both dedicated data thresholds and common datathresholds. If there is only one, it is the final data threshold.Alternatively, if there are both dedicated data thresholds and commondata thresholds, the common data threshold is the final data threshold,and if there is only one, it is the final data threshold.

The final reference signal received power threshold is a higher of thededicated reference signal received power threshold and the commonreference signal received power threshold or the dedicated referencesignal received power threshold, if there are both dedicated referencesignal received power threshold and common reference signal receivedpower threshold. If there is only one, it is the final data threshold.Or, if there are both dedicated reference signal received powerthreshold and common reference signal received power threshold, thecommon reference signal received power threshold is the final referencesignal received power threshold, and if there is only one, it is thefinal data threshold.

When at least one of the first condition sets is satisfied and all ofthe second condition sets are satisfied, that is, when both the firstresume procedure and the second resume procedure are triggered, theterminal selects the second resume procedure.

In step 2 a-23, the terminal performs a first resume procedure or asecond resume procedure with the base station.

FIG. 2B is a diagram illustrating a first resume procedure and a secondresume procedure according to an embodiment of the present invention.

The first resumption procedure is as follows.

In step 2 b-11, the terminal performs the first resume operation set 1.The first resume operation set 1 is operations taken when the firstresume procedure is started, and as follows. By performing the firstoperation set 1, the terminal may receive a downlink control messagefrom the base station through SRB1.

<First Resume Operation Set 1>

1. Apply default SRB1 configuration.

2. Apply default MAC Cell Group configuration

3. Start T319 set to t319 received from SIB1.

The default SRB1 configuration is as follows.

TABLE 5 Value Name SRB1 SRB2 SRB3 PDCP-Config >t-Reordering infinityRLC-Config CHOICE Am ul-AM-RLC >sn-FieldLength size12 >t-PollRetransmitms45 >pollPDU infinity >pollByte infinity >maxRetxThreshold t8dl-AM-RLC >sn-FieldLength size12 >t-Reassembly ms35 >t-StatusProhibitms0  logicalChannelIdentity 1 2 3 LogicalChannelConfig >priority 1 31 >prioritisedBitRate infinity >logicalChannelGroup 0

The default MAC Cell Group configuration is as follows.

TABLE 6 Name Value MAC Cell Group configurationbsr-Config >periodicBSR-Timer sf10 >retxBSR-Timer sf80phr-Config >phr-PeriodicTimer sf10 >phr-ProhibitTimersf10 >phr-Tx-PowerFactorChange dB1

T319 set to t319 is a timer to perform follow-up measures, for example,transition to RRC_IDLE, etc., when the first resume procedure fails.T319 set to t319 is stopped when RRCResume is received. If the RRCResumeis not received until the T319 set to t319 expires, the terminalperforms the T319 expiration operation set.

<T319 Expiration Operation Set>

1. Reset MAC.

2. Discard UE Inactive AS Context.

3. Release suspendConfig.

4. Discard the security key.

5. Release all RLC entities, PDCP entities, and SDAP entities.

6. Transition to RRC_IDLE and perform cell selection operation.

In step 2 b-13, the terminal performs the first resume procedureoperation set 2. The first resume procedure operation set 2 isoperations taken before transmitting the ResumeRequest.

<First Resume Procedure Operation Set 2>

0. Restore RRC configurations of UE Inactive AS context exceptmasterCellGroup and PDCP-config.

1. ResumeMAC-I calculation: Calculate a 16-bit message verification codeusing the first security key (a security key used in the RRC_CONNECTEDstate or a security key used at the time of receiving RRC Release).

2. Deriving the second base station security key using the second basestation security key. From the second base station security key, thesecond security key, the third security key, the fourth security key,and the fifth security key are derived.

3. All radio bearers except SRB0 are configured to use second securitykey and third security key or fourth security key and fifth securitykey.

3. Reset the PDCP entity of SRB1.

4. Resume SRB1.

In step 2 b-15, the terminal transmits a ResumeRequest message to thesecond base station. The MAC PDU containing the ResumeRequest messagedoes not include data from other radio bearers. ResumeRequest includesthe information below.

<ResumeRequest>

1. The first identifier or the second identifier: an identifierindicated in the system information among the first and secondidentifiers given in SuspendConfig is included.

2. ResumeMAC-I: 16-bit message verification code to ensure integrity ofthe resume request message. The terminal calculates the resume MAC-Iusing the previous security key (a security key used in theRRC_CONNECTED state or a security key used at the time of receiving theRRC Release).

3. resumeCause: Indicating one of emergency, highPriorityAccess,mt-Access, mo-Signalling, mo-Data, mo-VoiceCall, mo-VideoCall, mo-SMS,ma-Update, mps-PriorityAccess, mc s-PriorityAccess and smallDataTransfer

The terminal performing the first resume procedure selects one of theremaining values except for smallDataTransfer as the resumeCause. Thisis to enable the base station to determine whether the second resumeprocedure is performed through the resumeCause.

In step 2 b-17, the terminal receives the RRC Resume. RRCResume includesthe following information.

<RRCResume>

1. MasterCellGroup: CellGroupConfig for masterCellGroup includes RLCbearer information, MAC configuration information, PHY configurationinformation, and SpCell configuration information.

2. RadioBearrConfig: It is radio bearer configuration information andincludes SRB configuration information and DRB configurationinformation.

In step 2 b-19, the terminal performs the first resume procedureoperation set 3.

<First Resume Procedure Operation Set 3>

1. Stop T319.

2: Stop T380.

3: Restore and apply masterCellGroup of UE Inactive AS Context

4: Apply CellGroupConfig and radioBearerConfig in RRCResume

5. Resume SRB2, SRB3, and all DRBs.

6. Transition to RRC_CONNECTED state.

7. Stop cell reselection procedure.

In step 2 b-21, the terminal transmits an RRCResumeComplete message tothe second base station. The RRCResumeComplete message includes PLMNidentifier information selected by the terminal.

In step 2 b-23, the terminal and the second base station transmit andreceive data. In this case, the terminal may transmit a MAC CE such asBSR or PHR to the base station together. When the BSR trigger conditionis satisfied, the terminal multiplexes the BSR in the uplink MAC PDU andtransmit the MAC PDU. When the PHR trigger condition is satisfied, theterminal multiplexes the PHR MAC CE in the uplink MAC PDU and transmitthe MAC PDU. BSR trigger conditions include arrival of new data withhigh priority and expiration of periodic timers. PHR trigger conditionsinclude change of reference signal received power more than a predefinedthreshold, activation of a new secondary cell, and the like.

In step 2 b-25, when data transmission/reception with the terminal iscompleted, the second base station transmits an RRC Release includingSuspendConfig to the terminal to transition the terminal to theRRC_INACTIVE state.

In step 2 b-27, the terminal receiving the RRCRelease message includingSuspendConfig starts T380.

The second resume procedure is as follows.

In steps 2 b-31, the terminal performs the second resume operationset 1. The second resume operation set 1 is operations taken when thesecond resume procedure is triggered as follows. By performing thesecond resume operation set 1, the terminal may receive a downlinkcontrol message from the base station through the SRB1 and transmituplink data of the radio bearer (or data transmission in the INACTIVEstate, or in which the second resume procedure is configured).

<Second Resume Operation Set 1>

0: Restore all RRC configuration of UE Inactive AS Context (includingradio bearer settings of the first set of bearers, masterCellGroup, andPDCP-config).

1. start T319ext set to t319ext

2. stop T380

3. ResumeMAC-I calculation: A 16-bit MAC-I is calculated using theprevious K_RRCint, that is, the first security key (K_RRCint used in theprevious RRC_CONNECTED state or K_RRCint used at the time of receivingRRCRelease).

4. Deriving the second base station security key using the first basestation security key and the NCC. From the second base station securitykey, the second security key, the third security key, the fourthsecurity key, and the fifth security key are derived.

5. Configure the first bearer set to apply the second security key andthe third security key or the fourth security key and the fifth securitykey.

6. Reset the PDCP entity of the first bearer set.

7. Resume the radio bearer of the first bearer set.

8. Stop cell reselection procedure

9. Start the second cell reselection procedure.

T319ext set to t319ext is a timer to perform follow-up measures, forexample, transition to RRC_IDLE, etc., when the second resume procedurefails. T319, T319ext, and T380 have the following characteristics.

TABLE 7 First reconfiguration T380 T319 Configured by RRCRelease SIB1Start Upon reception of RRCRelease After start of first reconfigurationprocedure, between the time point when configuration received from SIB1is applied and the time point when SRB1 resumes Stop Upon reception ofRRCResume Upon reception of RRCResume and before applying cell group andbefore applying cell group configuration configuration Upon expirationInitiating periodic RNA update in T319 expiry operation set the currentcell Second reconfiguration T380 T319ext Configured by RRCRelease SIB XStart Upon reception of RRCRelease After start of second reconfigurationprocedure, between the time point when SRB1 configuration stored in UEInactive AS Context is applied and the time point when SRB1 resumes StopAfter start of second Upon reception of RRCRelease or reconfigurationprocedure, before applying cell group between the time point whenconfiguration SRB1 configuration stored in UE Inactive AS Context isapplied and the time point when SRB1 resumes Upon expiration Determiningwhether to initiate T319ext expiry operation set periodic RNA update inthe current cell

In the first resume procedure, T380 and T319 stops before configuringcell group information after receiving the RRCResume message to preventunnecessary subsequent operation due to the timer expiration by stoppingthe timers as a first operation after receiving the RRCResume message.

In the first resume procedure, starting T319 between the time point whenthe default SRB1 configuration is applied and the time point when SRB1resumes is to start T319 as close as possible to the time point whenSRB1 becomes available.

In the second resume procedure, starting T319ext between the time pointwhen SRB1 configuration stored in UE Inactive AS Context is applied andthe time point when SRB1 resumes is to start T319ext as close aspossible to the time point when SRB1 becomes available.

In the second resume procedure, starting T380 between the time pointwhen SRB1 configuration stored in UE Inactive AS Context is applied andthe time point when SRB1 resumes is to start T380 as close as possibleto the time point when T319ext starts so that the processing load fortimer handling in UE is reduced.

The time point when SRB1 configuration stored in UE Inactive AS Contextis applied and the time point when radio bearer configuration for firstbearer set stored in UE Inactive AS Context is applied are same.

If the RRCResume is not received until the T319ext set to t319extexpires, the terminal may perform the T319ext expiration operation setor the T319 expiration operation set. The base station may set inSuspendConfig or in system information which one to select between theT319ext expiration operation set and the T319 expiration operation set.

<T319ext expiration operation set>

1. Reset MAC

2. Keep UE Inactive AS Context

3. Keep suspendConfig

4. Discard first base station security key and first security key in UEand store second base station security key and third security key

5. Suspend all SRBs and DRBs

6. Start T380 set to t380

7. Stop second cell reselection procedure

8. Start cell reselection procedure

9. Perform RNA update after selecting a suitable cell

The first bearer set is a set of radio bearers for which the secondresume procedure is explicitly or implicitly configured and consists ofSRB1 and radio bearers related to the second resume procedure. The radiobearer related to the second resume procedure refers to a radio bearerin which the second resume procedure is explicitly allowed or a radiobearer in which the second resume procedure is explicitly configured.

Stopping the cell reselection procedure means stopping the existing cellreselection procedure performed before the second resume procedurestarts.

UE preferentially selects, in the existing cell reselection procedure, afrequency to camp on by considering cell reselection priority providedby base station, ranks each cell of the selected frequency byconsidering reference signal received power and various offsets, andreselects a highest ranked cell.

When the second cell reselection procedure starts, the terminal stopsusing the cell reselection priority and offsets indicated by the basestation and uses the following parameters.

<Second Cell Reselection Procedure>

1. Increase the cell reselection priority of the current servingfrequency to the highest priority.

2. Increase the first Qhyst by a predetermined value. Or apply the 2ndQhyst.

When the terminal determines the cell ranking, the current serving cellis weighted by Qhyst. That is, the ranking is determined by adding Qhystto the reference signal received power of the current serving cell. Thefirst Qhyst is included in the SIB2 and broadcasted. The second Qhyst orthe predetermined value is included in the SIBX and broadcasted.

In steps 2 b-33, the terminal transmits a MAC PDU including a first SDUincluding a ResumeRequest message and data of first bearer set (or dataof a bearer in which a second resume procedure is configured) to thesecond base station. The terminal performing the second resume procedureselects smallDataTransfer as ResumeCause. The terminal may include apriority-based BSR MAC CE and a PHR MAC CE in the MAC PDU. If theBSR/PHR inclusion condition is satisfied and the BSR/PHR cancellationcondition is not satisfied, the terminal includes and transmits thepriority-based BSR MAC CE and the PHR MAC CE in the MAC PDU. Theterminal transmits MAC PDUs that do not include the priority-based BSRand PHR when the BSR/PHR cancellation condition is satisfied even if theBSR/PHR inclusion condition is satisfied.

<BSR/PHR Inclusion Condition>

There is more data for transmission after transmission of the MAC PDU(or first uplink MAC PDU of the second resume procedure) includingResumeRequest, or uplink grant (or first uplink grant of the secondresume procedure) for transmission of MAC PDU including ResumeRequestdoes not accommodate all pending data available for transmission.

<BSR/PHR Cancellation Condition>

An uplink grant (or the first uplink grant of the second resumeprocedure) for transmission of MAC PDU including ResumeRequest canaccommodate all pending data available for transmission if at least oneof a triggered BSR and corresponding subheader or a triggered PHR arenot included in the MAC PDU but cannot accommodate all pending dataavailable for transmission if both triggered BSR and correspondingsubheader and triggered PHR and corresponding PHR are included in theMAC PDU.

In steps 2 b-35, the terminal and the base station transmit and receivedata of the first bearer set. Data of the first bearer set is scheduledby C-RNTI, and the terminal monitors a frequency region and a timeinterval, indicated in SIBX, for transmitting and receiving smallamounts of data (or for transmitting and receiving data in the secondresume procedure).

When the data transmission is completed, the base station determines toterminate the second resume procedure.

In steps 2 b-37, the second base station transmits an RRCReleaseincluding SuspendConfig to the terminal to terminate the second resumeprocedure. When receiving an RRCRelease including SuspendConfig, theterminal performs the second resume procedure operation set 2 toterminate the second resume procedure.

<Second Resume Operation Set 2>

1. Stop monitoring frequency region and time interval for small datatransmission

indicated in SIBX

2. Reset MAC

3. Update suspendConfig

4. Discard first base station security key and first security key in UEand store second base station security key and third security key

5. Suspend all SRBs and DRBs except SRB0

6. Start T380 set to t380

7. Stop second cell reselection procedure

8. Start cell reselection procedure

FIG. 2C is a diagram illustrating a structure of an uplink MAC PDU usedin a second resume procedure.

The MAC SDU (first SDU) (2 c-15) including the ResumeRequest message islocated at the front of the MAC PDU (2 c-11) and the MAC SDU (secondSDU) (2 c-19) including the data of the first bearer set (data of thebearer where second resume procedure is configured) is located at therear of the MAC PDU. This is to enable the base station receiving theMAC PDU to recognize as quickly as possible that the MAC PDU is a MACPDU related to the second resume procedure. The first SDU includes apart of the MAC-I calculated by the first security key (K_RRCintpreviously used), and the second SDU includes a MAC-I calculated by thefifth security key (new K_UPenc derived from the second base stationsecurity key). The MAC sub-header 2 c-13 of the first SDU includes two Rbits and an LCID field, and the MAC sub-header 2 c-17 of the second SDUincludes one R bit, an F field, an LCID field, and an L field. The LCIDfield indicates which logical channel the corresponding MAC SDU belongsto or which MAC CE is the corresponding MAC CE, and the L fieldindicates how many bytes the corresponding MAC SDU or MAC CE is. A MACSDU or MAC CE and corresponding MAC subheader is referred to as a MACsubPDU. The MAC PDU 2 c-11 shown in 2 c includes two MAC subPDUs 2 c-21and 2 c-23. Hereinafter, a structure of the MAC PDU shown in FIG. 2C isreferred to as a MAC PDU structure 1. MAC PDU structure 1 ischaracterized in that a MAC subPDU including a MAC SDU and having anR/LCID subheader locates in front of a MAC subPDU including a MAC SDUand having R/F/LCID/F. This feature allows the base station to processthe ResumeRequest message as soon as possible, as described above.

FIG. 2D is a diagram illustrating a structure of a general uplink MACPDU. Although a MAC PDU including two MAC subPDUs is exemplified, oneMAC PDU may include two or more MAC subPDUs. Hereinafter, a structure ofthe MAC PDU shown in FIG. 2D is referred to as a MAC PDU structure 2. InMAC PDU structure 2, a MAC subPDU having an R/LCID subheader is locatedbehind a MAC subPDU including a MAC SDU with an R/F/LCID/F subheader.MAC subPDUs with R/LCID subheaders correspond to MAC CE in most cases,and by placing MAC subPDUs including MAC CE behind MAC subPDUs includingMAC SDUs, the terminal can process MAC subPDUs including MAC SDUs inadvance before receiving uplink grant.

The first SDU 2 c-15 is a first RRC control message received by the basestation. Therefore, the base station and the terminal need to processthe first SDU by applying the same configuration without priorconsultation. On the other hand, the second SDU 2 c-20 may be processedafter the base station processes the first SDU and may be processedafter the base station restores the UE Inactive AS Context. Accordingly,the second SDU may be processed according to the configuration stored inUE Inactive AS Context.

In the present invention, a first configuration is applied to the firstSDU and a second configuration is applied to the second SDU. The firstconfiguration refers to a configuration predetermined in the standard(or a configuration standardized with one value), and the secondconfiguration refers to a configuration stored in the UE Inactive ASContext. Usually, one MAC PDU includes only the MAC SDU to which thefirst configuration is applied or only the MAC SDU to which the secondconfiguration is applied, but in the present invention, the MAC SDU towhich the first configuration is applied and the MAC SDU to which thesecond configuration is applied are transmitted together in a single MACPDU. This is to more quickly transmit the MAC SDU to which the secondconfiguration is applied.

The first configuration and the second configuration may include atleast PDCP configuration, RLC configuration, and logical channelconfiguration. The PDCP configuration of the first configuration is PDCPunused, the RLC configuration of the first configuration is RLCTM, thelogical channel configuration of the first configuration is the highestpriority, LCG ID 0, LCID 0, etc. Alternatively, the first configurationmay be a default SRB1 configuration.

The second configuration of a bearer where the second resume procedureis configured is as follows. The PDCP configuration is the PDCPconfiguration of the corresponding bearer stored in the UE Inactive ASContext, the RLC configuration is the RLC configuration of the RLCbearer associated with the corresponding bearer stored in the UEInactive AS Context (e.g., various timer values), and the logicalchannel configuration is the RLC bearer's logical channel configuration.The terminal applies, to the PDCP configuration and the RLCconfiguration, the configuration stored in the UE Inactive AS Context asit is. The terminal applies, to the logical channel configuration, onlysome of the configurations stored in the UE Inactive AS Context and doesnot apply the rest as if they were not configured. The logical channelconfiguration of the radio bearer belonging to the first bearer setconsists of an LCID, an LCG ID, a priority, and variousrestriction-related configurations. In transmitting data of the firstbearer set during the second resume procedure, the terminal uses storedvalues and processes various restriction-related configurations as ifthey were not configured. Various restriction-related configurationsinclude, for example, allowedServingCells, allowedSCS-List, andmaxPUSCH-Duration. If this restriction-related configuration is notconfigured, the terminal determines that there is no restriction on thecorresponding logical channel in transmitting and receiving data of thelogical channel. The stored restriction-related configuration may beapplied when the first resume procedure is initiated.

When the first SDU (2 c-15) and the second SDU (2 c-19) are multiplexedin one MAC PDU during the second resume procedure, the terminal appliesa predefined configuration for the first SDU, that is, PDCP not used,RLC TM, highest priority, LCID0 and LCG ID0. The terminal applies, tothe second SDU, overall PDCP configuration of the corresponding bearer,overall RLC configuration of the RLC bearer of the corresponding bearerand some of logical channel configuration of the RLC bearer of thecorresponding bearer stored in UE Inactive AS Context and does not applythe rest of logical channel configuration of the RLC bearer of thecorresponding bearer. The applied logical channel configuration may bean LCID, a priority and an LCG ID, and the non-applied logical channelconfiguration may be allowedServingCells, allowedSCS-List,maxPUSCH-Duration, and the like.

The terminal generates SDU1 by applying the first configuration, andgenerates SDU2 by applying the second configuration.

The uplink MAC PDU may include a MAC SDU or a MAC CE. The MAC CEcollectively refers to control information generated and transmitted bya MAC layer such as BSR or PHR. MAC CE may have a fixed size or avariable size. The field L is not used for the MAC subheader of the MACCE having a fixed size. A general MAC SDU has a variable size and an Lfield is used for a corresponding sub header. The MAC subPDU includingthe MAC CE is always located behind the MAC subPDU including the MACSDU. Therefore, in a general uplink MAC PDU in which at least two MACsubPDUs are multiplexed, a MAC subPDU having an L field is located infront and a MAC subPDU having no L field is located in rear. In general,all MAC SDUs included in one uplink MAC PDU are protected by a securitykey derived from the same base station security key.

FIG. 2E is a diagram illustrating a hierarchical structure of securitykeys.

The terminal and the base station perform integrity protection andciphering using security keys derived from the KgNB 2 e-11. Foursub-security keys, K_UPenc (2 e-21), K_UPint (2 e-23), K_RRCenc (2 e-25)and K_RRCint (2 e-27) are derived from KgNB (2 e-21). KgNB derives KgNB*(2 e-33) by inputting NCC (2 e-31) or the like during a handover orresume procedure, and new sub-security keys are derived from the KgNB*.

In FIG. 2C, the first SDU (2 c-15) is integrity protected by K_RRCintderived from KgNB used in the previous cell, that is, at least a part ofthe MAC-I calculated by the K_RRCint is included in the first SDU andtransmitted together, and the second SDU (2 c-19) is integrity protectedby K_UPint and ciphered by K_UPenc among sub-security keys of KgNB*derived from NCC and KgNB used in the previous cell.

That is, some of the MAC SDUs included in one MAC PDU during the secondresume process are protected by a security key derived from KgNB, andthe other MAC SDU is protected by a security key derived from KgNB*.

MAC SDUs multiplexed in the MAC PDU 2 d-11 of FIG. 2D are ciphered orintegrity protected by a sub-security key derived from one of KgNB andKgNB*.

KgNB previously used or used at the time of receiving RRCRelease is thefirst base station security key. K_RRCint derived from the first basestation security key is the first security key. KgNB* (or derived fromthe first base station security key and NCC or KgNB derived from thesecond resumption procedure operation set 1) is the second base stationsecurity key. K_RRCenc, K_RRCint, K_UPenc and K_UPint derived from thesecond security key are denoted as the second security key, the thirdsecurity key, the fourth security key and fifth security key.

Conventionally, one MAC PDU is ciphered or integrity protected withsecurity keys derived from one base station security key. In the presentinvention, by multiplexing MAC SDUs protected with security keys derivedfrom different base station security keys into one MAC PDU, the MAC SDUsare transmitted more quickly.

FIG. 2H is a diagram illustrating a MAC-I calculation process andciphering process.

The transmitting end 2 h-01 generates MAC-I and transmits the MAC-I tothe receiving end 2 h-02. The transmitting end generates MAC-I (2 h-23)by inputting the security key (2 h-19), COUNT (2 h-11), message (2h-13), DIRECTION (2 h-15), and BEARER (2 h-17) into the NIA (NRIntegrity Algorithm) (2 h-21) and transmits the generated MAC-I (2 h-23)to the receiving end.

The receiving end also calculates XMAC-I (2 h-25) by inputting thesecurity key (2 h-19), COUNT (2 h-11), message (2 h-13), DIRECTION (2h-15), and BEARER (2 h-17) into the NR integrity algorithm (NIA 2 h-21),and determines that the received MAC-I is the same. MAC-I and XMAC-I maybe the same only when the same NR integrity algorithm (NIA 2 h-21), thesame security key (2 h-19), the same COUNT (2 h-11), the same message (2h-13), the same DIRECTION (2 h-15), and the same BEARER (2 h-17) areused at the transmitting end and receiving ends. MAC-I has a 32-bitsize.

MAC-I included in the first SDU 2 c-15 of the uplink MAC PDU 2 c-11 ofthe second resume process is the last 16 bits of MAC-I calculated usinga first security key, a COUNT set to all Os, a DIRECTION set to 0 and amessage consisting of an identifier of a terminal and an identifier of acell.

The MAC-I included in the second SDU (2 c-19) of the uplink MAC PDU (2c-11) of the second resume process is for a PDCP SDU belonging to thefirst bearer set, and is calculated using a fifth security key, a COUNTof the PDCP SDU, a DIRECTION set to 0, and a DRB identifier, and amessage that is the PDCP SDU.

The transmitting end 2 h-31 processes a simple text to a ciphered blockas follows and transmits the same to the receiving end 2 h-32. Thetransmitting end generates a keystream block (2 h-53) by inputting asecurity key (2 h-49), a COUNT (2 h-41), a BEARER (2 h-43), a DIRECTION(2 h-45), and a LENGTH (2 h-47) into the NR Encryption Algorithm (NEA)(2 h-51). The transmitting end generates a ciphered block 2 h-35 byapplying exclusively OR calculation to the generated keystream blockwith simple text 2 h-33, and transmits the generated ciphered block tothe receiving end. The LENGTH is the length of the simple text.

The receiving end inversely converts the received ciphered block intosimple text using the same input and the same security key.

The second SDU 2 c-19 of the uplink MAC PDU 2 c-11 of the second resumeprocess may include a ciphered PDCP SDU of the first bearer set. ThePDCP SDU is ciphered using a fourth security key, a COUNT of the PDCPSDU, a DIRECTION set to 0, a DRB identifier BEARER, and a PDCP SDUlength LENGTH.

FIG. 2F is a diagram illustrating structures of a first BSR MAC CE and asecond BSR MAC CE, which are BSR based on a logical channel group.

The first BSR MAC CE includes one logical channel group identifier field2 f-01 and one first buffer size field 2 f-03. The logical channel groupidentifier field 2 f-01 has a size of 3 bits and indicates one of thelogical channel group identifiers between 0 and 7. The first buffer sizefield 2 f-03 has a 5-bit size and indicates one of the first buffer sizeindexes between 0 and 31. The first buffer size index 0 means that thereis no data available for transmission in the logical channels belongingto the corresponding logical channel group. The first buffer size index31 means that the sum of data available for transmission of the logicalchannels belonging to the corresponding logical channel group is greaterthan the 30th first buffer size. The first buffer size index 1 meansthat sum of data available for transmission of the logical channelsbelonging to the corresponding logical channel group is greater than 0and less than or equal to the first buffer size. The first buffer sizeindex n (2<=n<=30) indicates that sum of data available for transmissionof the logical channels belonging to the corresponding logical channelgroup is greater than or equal to the n−1th first buffer size and lessthan or equal to the nth first buffer size. The 30 first buffer sizesare defined in the standard.

The second BSR MAC CE includes eight LCGi bits 2 f-11 and a plurality ofsecond buffer size fields 2 f-13. The LCGi bit indicates whether asecond buffer size field exists for the logical channel group i. Forexample, it indicates whether a second buffer size field exists for LCG1logical channel group 1. If this field is 1, a second buffer size fieldexists for the corresponding LCG. The second buffer size field has an8-bit size and indicates one of the second buffer size indexes between 0and 255. The second buffer size index 0 means that there is no dataavailable for transmission in the logical channels belonging to thecorresponding logical channel group. The second buffer size index 254means that the sum of data available for transmission of the logicalchannels belonging to the corresponding logical channel group is greaterthan the 253rd second buffer size. The second buffer size index 1 meansthat sum of data available for transmission of the logical channelsbelonging to the corresponding logical channel group is greater than 0and less than or equal to the first second buffer size. The secondbuffer size index n (2<=n<=253) indicates that the sum of data availablefor transmission of the logical channels belonging to the correspondinglogical channel group is greater than or equal to the n−1th secondbuffer size and less than or equal to the nth second buffer size. Thesecond buffer size index 255 is not used. The 252 second buffer sizesare defined in the standard.

The logical channel group is configured when the logical channel isconfigured. The logical channel and the logical channel group areconfigured by RRC control messages.

FIG. 2G is a diagram illustrating structures of a third BSR MAC CE and afourth BSR MAC CE, which are priority-based BSRs. The third BSR MAC CEincludes one priority identifier field 2 g-01 and one third buffer sizefield 2 g-03. The priority identifier field has a size of 4 bits. Thepriority identifier field indicates one value between 0 and 15, whichcorresponds one-on-one to the logical channel priority between 1 and 16.That is, adding 1 to the value of the priority identifier field is equalto the actual priority. For example, the priority identifier field 0000means priority 1, 0001 means priority 2, and 1111 means priority 16. Thethird buffer size field indicates a third buffer size index between 0and 15 with a 4-bit size. Unlike the first buffer size index 0 or thesecond buffer size index 0, the third buffer size index 0 means that thesum of data available for transmission of the logical channels having acorresponding priority is equal to or greater than 0 and smaller thanthe first third buffer size. The third buffer size index n (2<=n<=14)indicates that the sum of data available for transmission of the logicalchannels having a corresponding priority is greater than or equal to then−1th third buffer size and less than or equal to the nth third buffersize. The third buffer size index 15 means that the sum of dataavailable for transmission of the logical channels having acorresponding priority is greater than the 15th third buffer size. Thefirst buffer sizes, the second buffer sizes, and the third buffer sizesare predefined in the specification. The 15 third buffer sizes aredefined in the standard.

The fourth BSR MAC CE includes PGi bits and a plurality of second buffersize fields.

PGi indicates whether a second buffer size field of the priority groupidentifier i exists. The priority group consists of at least onepriority, and eight groups could be configured from priority group 0 topriority group 7 in one cell. The priority for each logical channel isconfigured by a predetermined RRC control message received from thefirst NR cell, and the mapping relationship between the priority and thepriority group is configured by a predetermined system informationreceived from the second NR cell. The system information may be SIBX.For example, a list of priorities mapped per priority group may bebroadcast through the SIBX.

FIG. 3A is a flow diagram illustrating an operation of a terminal.

In step 3 a-01, the UE monitors whether the buffer status report istriggered. The UE proceeds to the next step when the buffer statusreport is triggered. The buffer status report is triggered when new dataarrives, the retransmission timer expires, or the periodic timerexpires.

In step 3 a-03, the UE determines which one to be generated between thebuffer status report including the priority identifier field and thebuffer status report including the logical channel group field. If thebuffer status report is triggered when the second resume procedure is inprogress or the buffer status report is triggered to the UE in theRRC_INACTIVE state, the base station receiving the buffer status reportcannot interpret the logical channel group identifier of the UE, so theUE first generates a priority identifier-based buffer status report.

The priority identifier-based buffer status report consists of a 4-bitpriority identifier field and a 4-bit buffer size field. The valueindicated in the priority field is one-to-one with the priority. Thevalue obtained by adding 1 to the indicated value in the priority fieldis the actual priority. The buffer size field contains informationrelated to the total amount of transmittable data having the priorityindicated in the priority field.

The logical channel group-based buffer status report consists of a 3-bitlogical channel group field and a 5-bit buffer size field.

The priority-based buffer status report and the logical channelgroup-based buffer status report use different LCIDs.

After generating the priority-based buffer status report, the UE startsa periodic timer and a retransmission timer. The periodic timer andretransmission timer apply a periodic timer value stored in MACconfiguration information of a terminal context and a retransmissiontimer value stored in MAC configuration information of a terminalcontext.

The priority identifier field of the priority-based buffer status reportis set to a value determined based on the priority stored in the logicalchannel configuration information of the terminal context.

When the second resume procedure is started, the terminal restores MACconfiguration information and logical channel configuration informationof the terminal context.

If there is at least one logical channel in which data to be transmittedexists and the priorities of the logical channels are different fromeach other, the terminal generates a buffer status report composed of apriority group identifier bitmap and a plurality of buffer size fields.The priority group can be configured for each cell and is configured bythe system information. The priority is configured for each terminal andis configured by an RRC control message.

In step 3 a-05, the terminal includes a first MAC subPDU including anuplink control message including a terminal identifier and a reason forresumption, a second MAC subPDU including data of the first bearergroup, and a third MAC including a buffer status report A MAC PDUincluding a subPDU is generated. The first MAC subPDU includes a firstMAC subheader and a first MAC SDU corresponding to the uplink controlmessage, and the second MAC subPDU includes a second MAC subheader and asecond MAC SDU corresponding to data of the first bearer group, and thethird MAC subPDU includes a third MAC subheader and a MAC CE.

The first MAC subheader is located immediately before the first MAC SDU,the first MAC SDU is located immediately before the second MACsubheader, the second MAC subheader is located immediately before thesecond MAC SDU, and the second MAC SDU is located immediately before thethird MAC subhead, the third MAC subheader is located immediately beforethe MAC CE.

A part of the first MAC subPDU is protected with a security key derivedfrom the first base station security key, a part of the second MACsubPDU is protected with a security key derived from the second basestation security key, and the third MAC subPDU is not protected.

In step 3 a-07, the terminal transmits the generated uplink MAC PDU.

In step 3 a-03, the terminal generates a buffer status report comprisinga logical channel group identifier field and a buffer size field if thesecond resumption procedure is not in progress. A buffer status reportcomposed of a priority identifier field and a buffer size field and abuffer status report composed of a logical channel group identifierfield and a buffer size field use different LCIDs.

After generating a buffer status report composed of an identifier fieldand a buffer size field, the UE starts a periodic timer and aretransmission timer to which the values stored in the UE Inactive ASContext are applied.

In the priority field, a value indicating a priority of a logicalchannel in which data to be transmitted is available is set, and thepriority is a priority of logical channel configuration information ofthe UE Inactive AS Context.

When there is more than one logical channel in which data to betransmitted exists and the priorities of the logical channels aredifferent, the terminal generates a buffer status report composed of apriority group bitmap and a plurality of buffer size fields. At thistime, the priority of the logical channel is set with the RRC controlmessage and the priority group is set with the system information.

FIG. 4A is a block diagram illustrating the internal structure of a UEto which the disclosure is applied.

Referring to the diagram, the UE includes a controller (4 a-01), astorage unit (4 a-02), a transceiver (4 a-03), a main processor (4 a-04)and I/O unit (4 a-05).

The controller (4 a-01) controls the overall operations of the UE interms of mobile communication. For example, the controller (4 a-01)receives/transmits signals through the transceiver (4 a-03). Inaddition, the controller (4 a-01) records and reads data in the storageunit (4 a-02). To this end, the controller (4 a-01) includes at leastone processor. For example, the controller (4 a-01) may include acommunication processor (CP) that performs control for communication andan application processor (AP) that controls the upper layer, such as anapplication program. The controller controls storage unit andtransceiver such that UE operations illustrated in FIG. 2A and FIG. 2Band FIG. 3A are performed.

The storage unit (4 a-02) stores data for operation of the UE, such as abasic program, an application program, and configuration information.The storage unit (4 a-02) provides stored data at a request of thecontroller (4 a-01).

The transceiver (4 a-03) consists of a RF processor, a basebandprocessor and plurality of antennas. The RF processor performs functionsfor transmitting/receiving signals through a wireless channel, such assignal band conversion, amplification, and the like. Specifically, theRF processor up—converts a baseband signal provided from the basebandprocessor into an RF band signal, transmits the same through an antenna,and down—converts an RF band signal received through the antenna into abaseband signal. The RF processor may include a transmission filter, areception filter, an amplifier, a mixer, an oscillator, adigital-to-analog converter (DAC), an analog-to-digital converter (ADC),and the like. The RF processor may perform MIMO and may receive multiplelayers when performing the MIMO operation. The baseband processorperforms a function of conversion between a baseband signal and a bitstring according to the physical layer specification of the system. Forexample, during data transmission, the baseband processor encodes andmodulates a transmission bit string, thereby generating complex symbols.In addition, during data reception, the baseband processor demodulatesand decodes a baseband signal provided from the RF processor, therebyrestoring a reception bit string.

The main processor (4 a-04) controls the overall operations other thanmobile operation. The main processor (4 a-04) process user inputreceived from I/O unit (4 a-05), stores data in the storage unit (4a-02), controls the controller (4 a-01) for required mobilecommunication operations and forward user data to I/O unit (905).

I/O unit (4 a-05) consists of equipment for inputting user data and foroutputting user data such as a microphone and a screen. I/O unit (4a-05) performs inputting and outputting user data based on the mainprocessor's instruction.

FIG. 4B is a block diagram illustrating the configuration of a basestation according to the disclosure.

As illustrated in the diagram, the base station includes a controller (4b-01), a storage unit (4 b-02), a transceiver (4 b-03) and a backhaulinterface unit (4 b-04).

The controller (4 b-01) controls the overall operations of the main basestation. For example, the controller (4 b-01) receives/transmits signalsthrough the transceiver (4 b-03), or through the backhaul interface unit(4 b-04). In addition, the controller (4 b-01) records and reads data inthe storage unit (4 b-02). To this end, the controller (4 b-01) mayinclude at least one processor. The controller controls transceiver,storage unit and backhaul interface such that base station operationillustrated in FIG. 2A and FIG. 2B are performed.

The storage unit (4 b-02) stores data for operation of the main basestation, such as a basic program, an application program, andconfiguration information. Particularly, the storage unit (4 b-02) maystore information regarding a bearer allocated to an accessed UE, ameasurement result reported from the accessed UE, and the like. Inaddition, the storage unit (4 b-02) may store information serving as acriterion to deter mine whether to provide the UE with multi—connectionor to discontinue the same. In addition, the storage unit (4 b-02)provides stored data at a request of the controller (4 b-01).

The transceiver (4 b-03) consists of a RF processor, a basebandprocessor and plurality of antennas. The RF processor performs functionsfor transmitting/receiving signals through a wireless channel, such assignal band conversion, amplification, and the like. Specifically, theRF processor up—converts a baseband signal provided from the basebandprocessor into an RF band signal, transmits the same through an antenna,and down—converts an RF band signal received through the antenna into abaseband signal. The RF processor may include a transmission filter, areception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC,and the like. The RF processor may perform a down link MIMO operation bytransmitting at least one layer. The baseband processor performs afunction of conversion between a baseband signal and a bit stringaccording to the physical layer specification of the first radio accesstechnology. For example, during data transmission, the basebandprocessor encodes and modulates a transmission bit string, therebygenerating complex symbols. In addition, during data reception, thebaseband processor demodulates and decodes a baseband signal providedfrom the RF processor, thereby restoring a reception bit string.

The backhaul interface unit (4 b-04) provides an interface forcommunicating with other nodes inside the network. The backhaulinterface unit (4 b-04) converts a bit string transmitted from the basestation to another node, for example, another base station or a corenetwork, into a physical signal, and converts a physical signal receivedfrom the other node into a bit string.

What is claimed is:
 1. A method by a terminal, the method comprising:receiving by a terminal from a first base station a RRCRelease message,the RRCRelease message includes a first information for a second resumeprocedure, the first information for a second resume procedure includesa SRB2 (Signaling Radio Bearer 2) indicator and a DRB (Data RadioBearer) list; determining by the terminal a first radio bearer groupbased on the first information for a second resume procedure; receivingby the terminal from a second base station a system information, thesystem information includes a second information for a second resumeprocedure, the second information for a second resume procedure includesa first threshold and a second threshold, the first threshold is relatedto a reference signal reception power and the second threshold isrelated to a data volume; initiating by the terminal the second resumeprocedure; re-establishing by the terminal PDCP entities of radiobearers of a second radio bearer group; resuming by the terminal radiobearers of the second radio bearer group; transmitting by the terminalto the second base station a RRCResumeRequest message; and receiving bythe terminal from the second base station a RRCResume message, wherein afirst resume procedure is to resume suspended RRC connection and thesecond resume procedure is for small data transmission in RRC_INACTIVEstate, and wherein the second radio bearer group is determined based onthe first radio bearer group.
 2. The method of claim 1, wherein thesecond resume procedure is initiated if all conditions in a firstcondition group are met, the first condition group includes a referencesignal reception power being greater than the first threshold and a datavolume being smaller than the second threshold and information relatedto the second resume procedure is included in the system information. 3.The method of claim 1, wherein a PDCP entity of the SRB1 isre-established and the SRB1 is resumed before the RRCResume message isreceived in case that the first resume procedure was initiated.
 4. Themethod of claim 1, wherein a SRB2 is a part of the first radio bearergroup in case that the SRB2 indicator is included in the firstinformation for a second resume procedure and the SRB2 indicator is setto a specific value, and wherein a DRB is a part of the first radiobearer group in case that the DRB Identity of the DRB is included in theDRB list.
 5. The method of claim 1, wherein the second radio bearergroup includes radio bearers of the first radio bearer group and theSRB1 if at least one radio bearer belongs to the first radio bearergroup.
 6. The method of claim 1, wherein a SRB1 is a part of the secondradio bearer group in case that at least one DRB ID is listed in the DRBlist or the SRB2 indicator is present.
 7. The method of claim 1, whereinthe SRB1 is implicitly configured with the second resume procedure basedon the status of other radio bearers, and wherein the SRB2 is explicitlyconfigured with the second resume procedure based on the SRB2 indicator,and wherein a SRB3 is implicitly not configured with the second resumeprocedure.
 8. The method of claim 1, wherein a PHR (Power HeadroomReport) is transmitted together with the RRCResumeRequest message in aMAC PDU.
 9. The method of claim 1, wherein a cause value indicatingsmall data transmission is indicated in RRCResumeRequest message in casethat the second resume procedure was initiated.
 10. The method of claim1, wherein the first base station and the second base station could be asame base station or different base stations.
 11. A terminal in awireless communication system, the terminal comprising: a transceiverconfigured to transmit and receive a signal; and a controller configuredto control the transceiver to: receive from a first base station aRRCRelease message, the RRC release message includes a first informationfor a second resume procedure, the first information for a second resumeprocedure includes a SRB2 indicator and a DRB list; determine a firstradio bearer group based on the first information for a second resumeprocedure; receive from a second base station a system information, thesystem information includes a second information for a second resumeprocedure, the second information for a second resume procedure includesa first threshold and a second threshold, the first threshold is relatedto a reference signal reception power and the second threshold isrelated to a data volume; initiate the second resume procedure;re-establish PDCP entities of radio bearers of a second radio bearergroup; resume radio bearers of the second radio bearer group; transmitto the second base station a RRCResumeRequest message; and receive fromthe second base station a RRCResume message, wherein the first resumeprocedure is to resume suspended RRC connection and the second resumeprocedure is for small data transmission in RRC_INACTIVE state, andwherein the second radio bearer group is determined based on the firstradio bearer group.
 12. A method by a base station, the methodcomprising: transmitting by a base station to a terminal a RRCReleasemessage, the RRC release message includes a first information for asecond resume procedure, the first information for a second resumeprocedure includes a SRB2 indicator and a DRB list; transmitting by thebase station a system information, the system information includes asecond information for a second resume procedure, the second informationfor a second resume procedure includes a first threshold and a secondthreshold, the first threshold is related to a reference signalreception power and the second threshold is related to a data volume;receiving by the base station from the terminal a RRCResumeRequestmessage; and transmitting by the base station to the second base stationa RRCResume message, wherein PDCP entities of radio bearers of thesecond radio bearer group are re-established in case that the secondresume procedure is initiated, and wherein radio bearers of the secondradio bearer group are resumed in case that the second resume procedureis initiated, and wherein PDCP entity of SRB1 is re-established in casethat the first resume procedure is initiated and wherein SRB1 is resumedin case that the first resume procedure is initiated.